The present technology generally relates to a method and apparatus for detecting and reporting magnetic fields in the proximity of a utility meter, and, more particularly the use of such technology in the context of improved meter tampering detection. The magnetic field sensors are adjustable allowing either remote or local sensitivity/selectivity adjustments to compensate for variations in the electromagnetic environments of different meter installation sites.
Utility meters, including solid state and electro-mechanical meters, have been in use for many years to measure the consumption of resources such as water, gas and electricity. Electric utilities, for example, use such utility meters to generate data indicative of the consumption of electric energy, which data is used for billing purposes. Traditionally, meter reading personnel would periodically inspect a customer installation to look for signs of tampering with the utility meter and to record meter readings, either manually or with the use of electronic devices (such as probes or receivers). Billing to the customer is established based on such collected data. Today, however, it has become increasingly common for such meters to have the capability of communicating with a central communication station. Such capability is often used for Automatic Meter Reading (AMR) where billing data is read remotely, eliminating the need for on-site data retrieval. Consequently, as the number of AMR equipped utility meters has increased, there has been a corresponding decrease in on-site inspections of such utility meters.
One adverse result of the increased use of AMR equipped utility meters is the increased opportunity for undetected tampering with the metering equipment. Tampering with a meter, such as an electricity meter, is an effort to defraud the electricity supplier of revenue to which it is rightfully entitled for the delivery of electric energy. One method of tampering with a utility meter is to subject the meter to a magnetic field. Electromagnetics embraces both electricity and magnetism and is basic to everything electric and magnetic. Thus, all electronic devices, including utility meters, can be adversely affected by spurious electromagnetic energy. In fact, many of the components used in modem solid-state electricity meters are sensitive to externally applied magnetic fields. If such fields are strong enough, these fields can reduce or eliminate altogether the meter's ability to measure the consumed energy.
Most, if not all, utility meter manufacturers test their products for immunity/susceptibility to electromagnetic fields and design their products to meet minimum immunity requirements set by regulatory agencies (such as the European Union). Should a utility meter be subjected to electromagnetic fields or magnetic fields that exceed the level for which such meter is design to withstand, the utility meter could be adversely affected. For example, magnetic fields produced by a magnet can have adverse affects on the accuracy of a utility meter.
Electric utility meters often employ current transformers to sense the current being drawn through the meter. The presence of a strong magnetic field may cause errors to be induced within the current transformers. As is well known to those skilled in the art, the meter could gain energy or lose energy depending on how the spurious magnetic field lines are linked through the current transformer.
Similarly, the magnetic components (e.g. transformer or coupled inductor, depending on the power supply topology used) within the utility meter power supply are also susceptible to electromagnetic/magnetic fields. Should a magnetic field saturate the magnetic components within the power supply of a utility meter, the meter may power down allowing energy to flow unmeasured.
In the past, to prevent magnetic tampering, ferrous metal cores and shields were used to block the magnetic fields within utility meters. Such shields and cores may not be the ideal magnetic tampering prevention solution, however, as such shields and cores are expensive and difficult to incorporate into new meter assemblies. Instead of shielding the electronics of a utility meter, a better solution would be to detect the existence of electromagnetic fields within the proximity of a utility meter. Consequently, there is a need to detect magnetic fields in the proximity of a utility meter.
Numerous utility meter tampering detection methods are known to those skilled in the art of manufacturing utility meters. One such method is described in U.S. Pat. No. 5,473,322 issued on Dec. 5, 1995 to Carney which discloses a mechanical based tamper detection method. Carney '332 discloses a device for detecting tampering of a utility meter that includes sensors to detect a positional displacement of the meter coupled with loss of power to the meter. On sensing a positional displacement of the meter, indicative of an attempt to remove the meter, a timer is activated to enable sensing a power loss to the meter within a predetermined amount of time. Another meter tampering detection method is described in U.S. Pat. No. 4,707,679 issued on Nov. 17, 1987 to Kennon, et al. which discloses using magnetically sensitive switches to sense the presence of a strong magnetic field in the region of a electric meter. One problem with such magnetic tamper detection methods is that the sensitivity may not be adjusted without making hardware changes to the utility meter.
Notably, electromagnetic energy may be either a natural or human made phenomena. Natural sources of electromagnetic energy include thunderstorms, the magnetic fields produced by magnets, and lighting discharges, to name only three. Electric-power generators, faulty electric-power transformers, electric-power transmission lines, broadcast communication electronics, radar, electric tools, electric machines and automobile-ignition systems are among human made electromagnetic energy sources. Considering the diversity of electromagnetic energy sources, it is unlikely that any two utility meters will be installed in environments where the undesired ambient electromagnetic energy levels are precisely equal. Consequently, a need exists for a method and apparatus for detecting magnetic fields in the proximity of a utility meter that is electrically programmable or adjustable so to allow remote or local adjustments to compensate for variations in the level of ambient electromagnetic activity or “pollution” at different utility meter installation sites.
In addition, the sensitivity of some magnetic sensors, such as magnetic reed switches, are not normally adjustable once such sensors have been manufactured. By using two or more of such sensors to detect magnetic fields over a wider area, the selectivity of such devices can be improved. Consequently, there is a need for a method of improving the selectivity of such magnetic sensors.